Sealing arrangement

ABSTRACT

Sealing arrangement for a piston rod with a circular cross-section, comprising a one-piece sealing ring with a parting joint and compensation clearance as well as a cover ring surrounding the sealing ring in the peripheral direction, with the sealing ring having a section which extends in the peripheral direction of the sealing ring at at one end and forms an overlapping ring joint together with the other end of the sealing ring, and with the sealing ring having a radial wall thickness decreasing towards the parting joint. This arrangement has an excellent sealing action in a direction axial to the arrangement.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The invention relates to a sealing arrangement comprising a one-piecesealing ring with a parting joint and compensating clearance and coverring surrounding or enclosing the sealing ring in the peripheraldirection.

2. Description of the Prior Art

Sealing arrangements for a body of circular cross-section such as apiston rod are known, in particular for piston compressors. Dry runningpiston compressors are machines which require no foreign lubrication inthe compression part. Such compressors have fixed sealing elements pastwhich a piston rod is moved. The seal elements are usually arranged oneafter the other in series and form in this manner a so-called packing. Apacking of this type with sealing arrangements and sealing rings isknown from CH 439 897. Sealing rings are subject to wear at the sealingsurface which lies against the piston rod. In order to maintain thesealing function over longer periods of time, the known sealing ring haswear compensation wherein the sealing ring is split up into threesealing ring elements with partial joints extending parallel to atangent with respect to the piston rod and with radial joints forming acompensatory ring gap. A hose spring peripherally surrounding thesealing ring exerts a preload on the sealing ring elements towards thepiston rod. This known sealing arrangement has the disadvantage that thesealing ring has a large number of partial joints, which impair thesealing function. In order to seal off these joints, a cover ring lyingin contact in the axial direction is arranged adjacent to the sealingring. Such a sealing arrangement has the disadvantage that it has arelatively long extent in the axial direction. A known problem of suchsealing arrangements at piston rods is the frictional heat which arises.Dissipation of the heat of friction via the seal elements themselves ispossible only with difficulty, since the seal elements are usually madeof plastic and act thermally almost as insulators. The greatest portionof the heat of friction is thus led off in a clearly less efficientmanner by the piston rod. The heat of friction which arises is thuslargely responsible for high wear, among other things, when sealingrings of plastic are used. Thus, a complicated and expensive cooling ofthe packing containing the sealing arrangement is often required.

SUMMARY OF THE INVENTION

It is the object of the present invention to overcome the disadvantagesof known sealing arrangements.

The sealing arrangement in accordance with the invention for a pistonrod with a circular cross-section thus comprises a one-piece sealingring with a ring gap and compensatory clearance as well as a cover ringsurrounding or enclosing the sealing ring in the peripheral direction,with the sealing ring having a section at least at one end which,together with the other end of the sealing ring, forms an overlappingring gap, and with the sealing ring having a wall thickness decreasingtowards the parting joint or ring gap respectively.

An advantage of the sealing arrangement in accordance with the inventionis to be seen in that the overlapping ring gap in the axial directionproduces a high degree of gas-tightness. The surrounding or enclosingcover ring assists the sealing action and exerts in addition a bias loadacting on the sealing ring towards the piston rod. The surrounding orenclosing cover ring seals the overlapping parting joint in the radialdirection.

Suitable materials for the sealing ring are plastics for dry runningapplications such as filled polymers with a matrix ofpolytetrafluoroethylene (PTFE) or a mixture of mechanically solid,high-temperature-resistant and wear-resistant polymers, which are alsodesignated as “high-temperature polymers”, such as poly(ether etherketone) (PEEK), poly(ether ketone) (PEK) polyimide (PI), poly(phenylenesulphide) (PPS), polybenzimidazole (PBI), polyamideimide (PAI) or alsoepoxy resin. The high-temperature polymers are not capable of dryrunning in their pure form and hence require additional solid lubricantssuch as carbon, graphite, molybdenum sulphide, PTFE etc. Suchhigh-temperature polymers are then designated as “modified”.

An advantage of the sealing arrangement in accordance with the inventionis to be seen in the fact that a sealing ring manufactured of ahigh-temperature polymer can, in particular, be used.

The term “high-temperature” polymer serves as a collective term inconnection with the use of sealing elements in piston compressors forplastics which are distinguished from the customary filled PTFEmaterials by the following properties:

High-temperature polymers have a high mechanical stability even at thehigh temperatures that are usual in dry running.

High-temperature polymers have no cold flow properties, so even finelyshaped sealing rings remain form-stable and, in particular, require noadditional support ring when used in a packing even at high pressures.

High-temperature polymers have a substantially higher module ofelasticity, which leads to greater stiffness for larger ring diametersof a sealing ring.

With high-temperature polymers, sealing rings can be manufactured which,in comparison with filled PTFE, have substantially smaller diameters andnevertheless a substantially higher mechanical loadability, so that suchsealing rings made of high-temperature polymers are suitable, inparticular, for use at high compression end pressures.

A previous disadvantage in the use of high-temperature polymers was tobe seen in the fact that the poor ability to adopt to a specific shapemade it difficult to achieve complete contact of the sealing ring overthe entire periphery of a piston rod, so that leaks resulted.

The sealing ring in accordance with the present invention has theadvantage that the sealing ring has a radial wall thickness whichdecreases towards the parting joint or the ring gap respectively, whichmeans that the sealing ring is made somewhat thinner and thus softer inbending in the region of the overlapping ring gap. By virtue of thisdesign, a sealing ring consisting of high-temperature polymers has goodshape matching ability.

The sealing ring in accordance with the invention is, in particular,suitable for dry running ring piston compressors, with the sealing ringpreferably consisting of a modified high-temperature polymer withso-called self-lubrication properties. A sealing ring of this type canbe manufactured as a very narrow ring so that, on the one hand, thepiston rod better transmits the heat via radiation heat to the packingand, on the other hand, a smaller frictional surface exists between thesealing ring and the piston rod, which reduces the heating up. In thismanner, an excessive heating up of the piston rod can be prevented,which has the additional advantage that the sealing ring is subject toreduced wear.

The sealing arrangement in accordance with the present invention has ahigh imperviousness so that only slight leakage occurs through thesealing arrangement, and the leakage takes place mainly between thepiston rod and the sealing surface of the sealing ring. During this, agas bearing arises between the piston rod and the sealing surface, whichreduces the production of heat and thus, in addition, the heating of thepiston rod as well as the wear on the sealing ring.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a perspective view of a sealing arrangement;

FIG. 2 is a plan view of a sealing ring;

FIG. 3 is a bottom view of the sealing ring;

FIG. 4 is a cross-section through the sealing ring;

FIG. 4a is a further cross-section through a sealing ring along the line(B—B);

FIG. 4b is a further cross-section through the sealing ring of FIG. 4aalong the line (C—C);

FIG. 5 is a further cross-section through a sealing ring and

FIG. 6 is a plan view of a cover ring;

FIG. 7 is a plan view of a further exemplary embodiment of a sealingring;

FIG. 7a is a side view of the sealing ring of FIG. 2 from the directionE;

FIG. 7b is a side view of the sealing ring of FIG. 7 from the directionE;

FIG. 8 is a longitudinal view through a dry running sealing arrangement.

DETAILED DESCRIPTION OF THE PREFERRED EXEMPLARY EMBODIMENTS

FIG. 1 shows an exploded view of a sealing arrangement 12 consisting ofa sealing ring 1, a cover ring 2 placed on the sealing ring 1 in thedirection of its periphery, as well as a hose spring or toroidal spring3 surrounding the cover ring 2 in the direction of its periphery. Theplan view of the sealing ring 1 shown in FIG. 2 has a surface 1 hextending in the form of a circle along the inner circle that faces thebody to be sealed, a piston rod 4, and performs a sealing function. Thesealing ring 1 is executed as a one-piece ring with a parting joint 1 aso that the sealing ring runs out into two ends 1 b, 1 c. The end 1 c isexecuted in such a manner that it has, as evident from the bottom viewin FIG. 3, a section 1 d extending in the peripheral direction of thesealing ring 1, which together with the other end 1 b forms a ring gapoverlapping in the peripheral direction. The sealing ring 1 has elasticproperties so that it has a clearance S in the region of the partingjoint 1 a. In the present exemplary embodiment, the sealing ring 1 isexecuted in such a manner that its radial wall thickness D continuallydecreases towards the parting joint 1 a beginning at the position Dmaxopposite the parting joint 1 a, that is, in the direction D1 or D2. Inthis manner, even a sealing ring which is manufactured of a materialwith a higher modulus of elasticity, such as a high-temperature polymerfor example, has a behavior which becomes increasingly more elasticand/or softer in bending towards the parting joint 1 a. The cover ring 2with a hose spring 3 surrounding the sealing ring 1 exerts a force onthe sealing ring 1 acting towards the piston rod. The cover ring 2 isexecuted as an open ring. By virtue of the clearance S at the partingjoint 1 a, as well as the elastic behavior towards the parting joint 1a, the sealing ring 1 has a good ability to adapt to the shape of thepiston rod 4 so that the sealing ring 1 sealingly surrounds the pistonrod 4 over its entire periphery. The sealing ring 1 has a surface 1 m, 1n facing outwards and extending in the form of a circle. In theexemplary embodiment, the profiles of the two surfaces 1 h, 1 m aremutually arranged in such a manner that they extend eccentric to oneanother. The sealing ring 1 has five back-flow grooves 4 a or pressurerelief grooves 4 a extending in the radial direction. These pressurerelief grooves 4 a enable (e.g. FIG. 8) a gas enclosed in the packingring chamber 14 to flow back into the cylinder during an intake strokeof the cylinder so that a doubly acting sealing function of the sealingelement 1, i.e., a sealing function both during the intake phase as wellas during the compression phase of the cylinder, is prevented. It isalso possible to execute a sealing ring 1 without back-flow grooves 4 a.Instead, back-flow grooves 4 a can be milled into the metallic base ofthe chamber ring 5, for example.

FIG. 6 shows an exemplary embodiment of an open cover ring 2 which has asector-shaped cut-out 2 a. The sealing ring 1 has a cylinder-shaped,projecting holding means 1 g which comes to lie in the cut-out 2 a whenthe cover ring 2 is placed onto the sealing ring 1, so that the coverring 2 is secured against rotation in the peripheral direction of thesealing arrangement 12.

FIG. 7a shows a side view of the sealing ring of FIG. 2 from thedirection E. The ring joint of the sealing ring has the two ends 1 b, 1c, with the end 1 b having the end section 1 d extending in theperipheral direction, so that a ring gap overlapping in the peripheraldirection results.

FIG. 5 shows a section through a sealing ring 1 along the line (A—A) inFIG. 2, with the parting joint 1 a being executed differently incomparison with the execution in accordance with FIGS. 1 to 3. At eachend 1 b, 1 c of the sealing ring 1, end sections 1 d, 1 e are placedextending in the peripheral direction of the sealing ring 1 whichoverlap in the peripheral direction and, in this manner, form anoverlapping ring joint. The parting joint 1 a again has a clearance S.The side view 7 b of t he sealing ring 1 corresponds to an embodiment inaccordance with FIG. 5 when viewed from the direction E. The sealingring 1 runs out into the two ends 1 b, 1 c which have end sections 1 d,1 e overlapping in the peripheral direction. Between the ends 1 b, 1 cthere results an intermediate space of width S1 and S2, respectively. Ina preferred embodiment, the two widths S1, S2 are made equally large sothat the sealing ring 1 has a clearance S=Si=S2 in the peripheraldirection. The cover ring 2 comes to lie in the recess 1 n, with therecess 1 n being made so wide that the recess 1 n also extends over theend section 1 e in the peripheral direction so that the cover ring 2encloses the end section 1 e in the region of the recess 1 n. A sealingarrangement 12 of this kind has a high sealing action since the coverring 2 encloses the intermediate space with the width S1, as well as thegap between the end sections 1 d, 1 e, which results in a highimperviousness in the radial direction. In addition, a mutual relativemovement of the two end sections 1 d, 1 e in the radial direction isprevented.

FIG. 4 shows a section through a sealing ring 1 along the line A—A inFIG. 2 with a further possibility for the design of the cross-section.The sealing ring 1 has a surface 1 h oriented towards a sliding surfaceof a piston rod 4. This surface 1 h has a height H in the axialdirection and is designed to extend cylindrically over a part 1 i inorder to form a sealing surface 1 i and is designed to diverge along afurther part 1 k. The diverging surface 1 l can be executed e.g. to beconically divergent at an angle β.

The sealing arrangement 12 in accordance with the present invention, hasan excellent sealing effect since a flow-through is prevented both inthe axial and in the radial direction. In this manner, gas constituentsescape mainly between the sealing surface 1 i and the sliding surface ofthe piston rod 4, which has the advantage that the sealing ring 1 caneasily be lifted off from the sliding surface and the friction is thusreduced. The divergent surface 1 l has the effect that the gasconstituents flow unimpeded in the direction towards the reduced sealingsurface 1 i, with the gas constituents exerting a force on the sealingring 1 which acts outwardly in the radial direction both on the surface1 l as well as on the surface 1 i. In this manner, a leakage between thesealing surface 1 i and the sliding surface of a piston rod 4 isfacilitated, whereby a gas bearing arises between the sealing ring 1 andthe piston rod 4. The sealing surface 1 i can be made relatively narrowin its axial extent in order to produce a pronounced gas bearing. Inthis manner, the friction between the sealing surface 1 i and the pistonrod 4 can be reduced, which has the advantage that both the heating upof and the wear on the sealing ring 1 are reduced. The sealing ring 1has a recess 1 n for receiving the cover ring 2. This recess 1 n canalso be executed in a different manner, or it may be absent.

FIG. 8 shows a longitudinal section through a dry running sealingarrangement or a so-called packing 6. To this belongs at least onesealing chamber 14 which surrounds the piston rod 4 and is formed of twochamber rings 5, and which is sealingly screwed to the associatedcylinder space 15. A two-part sealing ring disk 12 comprising a sealingring 1, as well as a cover ring 2, is placed in the sealing chamber 14.In addition, a hose spring 3 surrounds the cover ring 2. As a result ofthe sealing function of the ring 1, the pressure P1 in the compressionchamber 14 is greater than the pressure P2 in the passage opening to thefollowing compression chamber 14.

In distinction to the embodiment of FIG. 2, the exemplary embodiment ofa sealing ring 1 illustrated in FIG. 7 has a surface 1 h with acone-shaped partial surface 1 l. The partial surface 1 l is interruptedat three places by a web 1 p. It can also prove advantageous to arrangemore than three webs 1 p distributed about the periphery. FIG. 4a showsa section through the sealing ring 1 along the line B—B and shows thecone-shaped partial surface 1 l, which extends in the axial directionover a width 1 k, as well as the cylindrically extending partial surface1 i. The partial surface 1 l extending in a cone shape intersects thesurface of the piston rod 4 at an angle β. FIG. 4b shows a sectionthrough a web 1 p of the sealing ring 1 along the line C—C. A web 1 p isexecuted in such a manner that the inner surface 1 h has a width in theaxial direction corresponding to the width H of the sealing ring 1 andextends parallel to the piston rod 4. A web 1 p lies in contact with thepiston rod 4 over the entire width H and serves to stabalize the sealingring 1. The exemplary embodiment in accordance with FIG. 7 has threewebs 1 p arranged so that they are distributed over the periphery of thesurface 1 h, with a web 1 p being placed in the region of the partingjoint 1 a. A sealing ring 1 b can naturally also be executed withoutwebs 1 p so that the conical partial surface 1 l extends over the entireperiphery of the surface 1 h without interruption.

The conically extending partial surface 1 l has a maximum distance B tothe piston rod 4 in accordance with FIG. 4a. In an embodiment of thesealing ring 1, the clearance S is made so wide that it has a width of“2 times pi times B”. A sealing ring 1 executed in this manner forms afriction ring in a first phase of operation and a flow ring in a secondphase of operation, in the first phase of operation the sealing ring 1has a conically extending partial surface 1 l. With increasing wear atthe sealing surface 1 i the conically extending partial surface 1 l isdiminished until the sealing surface 1 i extends over the entire widthH. If the clearance S is made to correspond to a width of “2 times pitimes B”, then the clearance becomes zero as soon as the partial area 1l is completely abraded away. In this state, the sealing ring 1 becomesa flow ring because, since the play amounts to zero, hardly any furtherwear of the sealing surface 1 i results so that the sealing ring 1 hasan approximately constant leakage during the second phase of operation.The sealing ring 1 thus has a maximum flow resistance during the secondphase of operation.

The partial surface 1 l cannot only be executed to diverge conically,but can take on any arbitrary shape in such a manner that a spacingarises in the region of the partial surface 1 l between piston rod 4 andthe sealing ring 1.

What is claimed is:
 1. A sealing arrangement for a piston rod with acircular cross-section, comprising a one-piece sealing ring with aparting joint and compensation clearance as well as a cover ringsurrounding or enclosing the sealing ring in the peripheral direction,with the sealing ring having a section which extends in the peripheraldirection of the sealing ring at least at one end and forms anoverlapping ring joint together with another end of the sealing ring,and with the sealing ring having a radial wall thickness which decreasestowards the parting joint; wherein the sealing ring has at its radiallyouter surface a recess extending along the circumference of the sealingring, the cover ring fitting in the recess and a sealing surface whichis a radially inner surface of the sealing ring.
 2. A sealingarrangement in accordance with claim 1 wherein the sealing ring has acircularly extending surface oriented radially inwardly towards a bodyto be sealed; and wherein the sealing ring has a surface at its radiallyouter side extending circularly in the peripheral direction of thesealing ring and eccentric to the circularly extending surface.
 3. Asealing arrangement in accordance with claim 1 wherein the sealing ringhas a securing means in order to prevent a mutual rotation of thesealing ring and the cover ring.
 4. A sealing arrangement in accordancewith claim 1 wherein the cover ring has elastically resilient propertiesand surrounded by a spring lying on the cover ring and extending in theperipheral direction of the sealing ring.
 5. A sealing arrangement inaccordance with claim 1 wherein the sealing ring has a surface orientedradially inwardly towards a body to be sealed; wherein the surface has aheight in a direction extending perpendicular to the peripheraldirection of the sealing ring; wherein the surface is of cylindricalshape over a portion of the height in order to form a sealing surfaceand has a surface with a radius enlarged with respect to the sealingsurface over a further part.
 6. A sealing arrangement in accordance withclaim 5 wherein the surface is made conically divergent.
 7. A sealingarrangement in accordance with claim 5 wherein the surface diverges inthe radial direction by a maximum distance B; and wherein thecompensatory clearance has a width of times pi times B.
 8. A sealingarrangement in accordance with claim 5 wherein a plurality of webs arearranged distributed along an inner surface in the peripheral direction.9. A sealing arrangement in accordance with claim 1 wherein the sealingring is manufactured of one of a plastic or a modified high temperaturepolymer.
 10. A sealing arrangement in accordance with claim 9 whereinthe sealing ring is manufactured of one of polytetrafluoroethylene(PTFE), poly(ether ether ketone) (PEEK), poly(ether ketone) (PEK),polyimide (PI), poly(phenylene sulphide) (PPS), polybenzimidazole (PBI),or polyamideimide (PAI).
 11. A sealing arrangement in accordance withclaim 1 wherein the covering is surrounded by a spring lying on thecover ring and extending in the peripheral direction of the sealingring.
 12. A packing for sealing a piston rod with sealing arrangementsthat comprise: a one-piece sealing ring with a parting joint andcompensation clearance as well as a cover ring surrounding or enclosingthe sealing ring in the peripheral direction, with the sealing ringhaving a section which extends in the peripheral direction of thesealing ring at least at one end and forms an overlapping ring jointtogether with another end of the sealing ring, and with the sealing ringhaving a radial wall thickness which decreases towards the parting jointwherein the sealing ring has at its radially outer surface a recessextending along the circumference of the sealing ring, the cover ringfitting in the recess.
 13. A piston compressor with a sealingarrangement comprising: a packing for sealing a piston rod with sealingarrangements that comprise: a one-piece sealing ring with a partingjoint and compensation clearance as well as a cover ring surrounding orenclosing the sealing ring in the peripheral direction, with the sealingring having a section which extends in the peripheral direction of thesealing ring at least at one end and forms an overlapping ring jointtogether with another end of the sealing ring, and with the sealing ringhaving a radial wall thickness which decreases towards the parting jointwherein the sealing ring has at its radially outer surface a recessextending along the circumference of the sealing ring, the cover ringfitting in the recess.